Apparatus for controlling the activity of a reactor



A. HUET 3,140,981

APPARATUS FOR CONTROLLING THE ACTIVITY OF A REACTOR July 14, 1964 FiledSept. 12, 1958 INVENTOR. ANDRE HUET ATTORNEY nited tates te Thisinvention relates to nuclear reactors and particularly to control meanstherefor.

It is known to control the activity of nuclear reactors by means ofcontrol or safety rods of, for example, cadmium, which are loweredvertically, generally under their own weight, between the fuel rods ofthe reactor. Such an arrangement is applicable especially in the case ofland installations but is the cause of larger over-all dimensionsbecause of the accessories which must be provided above the reactor forsuspending and operating the control rods.

The present invention has for its object a nuclear reactor with controlapparatus operating inside the reactor and which can be applied tomobile reactor installations, such as marine installations.

According to the invention the reactor includes control apparatusconstituted by rods, or strips of sheet metal, disposed side by sideinside the reactor with their axes in a direction normal to the axes ofthe fuel rods, in which position they do not act to perform thecontrolling process. When it is desired to regulate the activity of thereactor, these rods or strips, which are articulated at one pointthereof, pivot either under the effect of their weight or under theeffect of a mechanical device and are spread out fan-wise between thefuel rods, in which position they assume a direction which is obliquewith respect to these rods.

It is provided that the dimensions of the rods and the cross-sectionsthereof may vary from one rod to the other, or even in the same rod, sothat in the control position they exert a greater action in those areasof the reactor where the liberation of neutrons is most dense.

The apparatus may be combined with any device for altering the distancesbetween the fuel rods, either mechanically or by vibration, and alsowith a method of controlling the activity of the reactor comprising thesuspension of metal particles absorbing neutrons in the fluidcirculating between the rods.

It is possible for the apparatus to be used only in one area of thereactor and even on only one part of the length of the fuel rods.

The following description when read with reference to the accompanyingdrawings, which illustrate an example of the invention, will make itpossible to understand how the invention can be carried into effect.

FIG. 1 is a diagrammatic vertical section of the apparatus mountedinside a reactor;

FIG. 2 is a diagrammatic plan view of the apparatus shown in FIG. 1;

FIGURES 3, 4 and relate to a form of construction of the suspension ofthe control strips:

FIG. 3 is a cross-section of the ends of the strips pivoting on a shaftand in the folded position;

FIG. 4 is a similar view showing the strips opened out fan-wise;

FIG. 5 is a section showing in plan the articulation of the strips tothe shaft.

As will be seen in FIG. 1, inside a reactor shell containing fuel rodsshown diagrammatically in chain-dotted lines at 12 in FIG. 1 and arerepresented by crosses in the plan view of FIG. 2, are mounted controlstrips or rods 14 which, in the operating condition of the pile, arepositioned normally to the axes of the fuel rods 12, as can be seen inthe left-hand part of FIG. 1. These rods ice 14 are pivotally mounted atone end on to a shaft 16 (FIG. 3).

When it is desired to control the reactivity of the pile or terminateit, the rods are spread out fan-wise as can be seen in the right-handpart of FIG. 1, so as to assume directions oblique with respect to theaxes of the fuel rods 12 and to be inserted between the latter in orderto absorb neutrons.

In the example shown, the rods 14 are mounted on each side in the pile10 and, in the spread position, form a screen or shield in asubstantially median plane AA of the pile. Of course, it is possible toprovide two screens of this kind inside the pile, or two screensdisposed at right angles, or any other arrangement which might provemore effective having regard to the distribution adopted for the fuelrods 12.

Movement of the control rods, for passing from the rest or inoperativeposition to the operative position, can be produced, as in the casedescribed, by gravity or alternatively by means of a suitable mechanicallinkage.

In the example shown in FIGS. 3 to 5, the control rods 14 are supportedin the inoperative position by a stop or lug 20 fast with a disc 22slipped on to the shaft 16. The shaft 16 and the disc 22 are controlledfor movement from the outside of the reactor by means of the knob 24abutting against the outside of the wall 10 of the reactor. Each of themoderating or control strips or rods 14 terminates in a hook 26 which isengageable with one of a set of fixed pins 28. The set of pins 28 issuitably distrib uted as can be seen in FIGS. 3 and 4, so that, in thecontrol position, the rods 14 are spread out fan-wise, as can be seen inFIG. 1 (righthand part). The pins 28 are adjustable in position in orderto regulate the degree of opening of the fan.

In order to bring the rods 14 back to the folded position (arrow F), itis necessary to rotate the shaft 16 by means of the knob 24 so that thestop 20, in moving back from the position shown in FIG. 4 to theposition shown in FIG. 3, raises the rods 14 one by one in successionand closes the fan formed thereby.

The lengths of the rods 14 are, for example, different, as can be seenin FIG. 5, so that those rods which are in the middle of the fan extendfurther into the pile. Likewise, the dimensions, of Width and thickness,of the rods 14 may be different, according to their positions, and mayvary along the same rod or strip. The rods 14 may have an ellipticalshape, as shown in the figures, so that a larger quantity of metalabsorbing the neutrons may be located in those areas of the pile wherethe flow of neutrons is greatest.

The device described above for moving the rods 14 relies on gravity andmay be replaced by a mechanical linkage ensuring the moving apart andthe folding back of the said rods whatever the position of the reactor10.

Instead of the rods 14 covering the entire height of the pile 10, asshown in the figures, they could cover only a certain part thereof andslow down the operation of the pile only over a certain length of thefuel rods 12.

What I claim is:

1. In a nuclear reactor having fuel rods disposed in a reactor shell,and an array of control rods or strips of neutron absorbing material forcontrolling the reactivity of said reactor mounted entirely inside thereactor shell and above the fuel rods, and means for maintaining therods or strips of neutron absorbing material in said array in fanlikepivoted relationship about a common pivot point and in a position withtheir axes normal to the axes of the reactor fuel rods, said means beingoperable for spreading out the control rods in fan-like manner betweenthe fuel rods when control is to be exercised over the reactivity of thereactor, and said control rods in said array each being of differentlength, and the planar cross-sections thereof varying from one to theother.

2. In a nuclear reactor having fuel rods disposed in a reactor shell,and an array of control rods or strips of neutron absorbing material forcontrolling the reactivity of said reactor mounted entirely inside thereactor shell and above the fuel'rods, and means for maintaining therods or strips of neutron absorbing material in said array in fan-likepivoted relationship about a common pivot point and in a position withtheir axes normal to the axes of the reactor fuel rods, said means beingoperable for spreading out the control rods in fan-like manner betweenthe fuel rods when control is to be exercised over the reactivity of thereactor and rods in said array each being of different length, and theplanar cross-sections thereof varying longitudinally to provide eachcontrol rod with a substantially elliptical planar configuration.

Zinn et al.: Nuclear Science and Engineering, vol. I (October 1956),pages 420, 423, 434, 435.

Nuclear Power, vol. 1 (September 1956), pp. 205-209.

1. IN A NUCLEAR REACTOR HAVING FUEL RODS DISPOSED IN A REACTOR SHELL,AND AN ARRAY OF CONTROL RODS OR STRIPS OF NEUTRON ABSORBING MATERIAL FORCONTROLLING THE REACTIVITY OF SAID REACTOR MOUNTED ENTIRELY INSIDE THEREACTOR SHELL AND ABOVE THE FUEL RODS, AND MEANS FOR MAINTAINING THERODS OR STRIPS OF NEUTRON ABSORBING MATERIAL IN SAID ARRAY IN FANLIKEPIVOTED RELATIONSHIP ABOUT A COMMON PIVOT POINT AND IN A POSITION WITHTHEIR AXES NORMAL TO THE AXES OF THE REACTOR FUEL RODS, SAID MEANS BEINGOPERABLE FOR SPREADING OUT THE CONTROL RODS IN FAN-LIKE MANNER BETWEENTHE FUEL RODS WHEN CONTROL IS TO BE EXERCISED OVER THE REACTIVITY OF THEREACTOR, AND SAID CONTROL RODS IN SAID ARRAY EACH BEING OF DIFFERENTLENGTH, AND THE PLANAN CROSS-SECTIONS THEREOF VARYING FROM ONE TO THEOTHER.